The specific aim of this search is to study the anatomical connections and organization of the corpus striatum and related nuclei in the monkey using anterograde and retrograde axonal transport technics. Studies will be directed towards determining: (1) the afferent and efferent projections of the subthalamic nucleus, (2) the origin of pallidofugal fiber systems and their relationships to thalamic relay nuclei, and (3) the afferent and efferent projections of the centromedian nucleus of the thalamus. Afferent projections to the subthalamic nucleus, thalamic relay nuclei and the centromedian nucleus will be determined by injections of small volumes of horseradish peroxidase (HRP) into these nuclei and studying the retrograde transport of this enzyme. The efferent projections of the subthalamic nucleus and the centromedian nucleus will be determined by injecting small volumes of (3H) amino acids (L-leucine and L-proline) into these nuclei by stereotaxic technics and studying the axoplasmic transport of these isotopes in autoradiographs of selected sections. Sections will be studied microscopically by bright and dark field illumination. The object of this study is to elucidate the neural mechanisms by which the corpus striatum and ralated nuclei make contributions to normal motor functions and to obtain insight into how pathological processes may disrupt these normal functions to produce dyskinesia and other abnormalities of motor function. BIBLIOGRAPHIC REFERENCES: Carpenter, M.B., Nakano, K. and Kim, R. 1976 Nigrothalamic projections in the monkey demonstrated by autoradiographic technics. J. Comp. Neurol., 165: 401-416. Jayaraman, A., Patt, J.A. and Carpenter, M.B. 1976 Projections of the corpus striatum and adjacent nuclei studied by autoradiographic technics. Anat. Rec., 184: 436 (Abstract).